Investigating the flyby scenario for the HD 141569 system

Context. HD 141569, a triple star system, has been intensively observed and studied because of its massive debris disk. Until recently, it was regarded as a gravitationally bound triple system but recent measurements of the HD 141569A radial velocity seem to invalidate this hypothesis. The flyby scenario therefore has to be further investigated to test its compatibility with the observed disk structures. Aims. We present a study of the flyby scenario for the HD 141569 system by considering 3 variants: a sole flyby, a flyby associated with one planet embedded in the disk and a flyby with two planets in the disk. We discuss the merits of each one to reproduce the scattered light observations of the disk. Methods. We first use analytical calculations to reduce the parameter space of the 2 stellar companion orbit and then perform N-body numerical simulations of the flyby encounter using symplectic integration, taking into account the gravitational influence of the stars and the planets on massless test particles. Results. The binary orbit is found to be almost fixed by the observational constraint on an edge-on plane with respect to the observers. If the binary had an influence on the disk structure, it should have a passing time at the periapsis between 5000 and 8000 years ago and a distance at periapsis between 600 and 900 AU. It also appears that the best scenario to reproduce the disk morphology is a flyby with 1 planet embedded in the disk. For a 2 M(J) planet, its orbital eccentricity must be around 0.2 while for a 8 M(J) planet, it must be below 0.1. In the two cases, its apoapsis is about 130 AU. Conclusions. Although the global disk shape is reasonably well reproduced, some observed features cannot be explained by the present model and the likehood of the flyby event remains an issue for the scenario explored in this paper. Dynamically speaking, HD 141569 is still a puzzling system.